Project Summary/Abstract Adults with autism spectrum disorder (ASD) often have poor outcomes across a range of domains, particularly emotional health. Rumination, or repetitive negative thinking, is a cognitive characteristic of ASD that also appears to contribute to depression and anxiety. Rumination is linked to both poor emotional and physical health in the general population. However, as perseveration is a core feature of autism, repetitive thinking (RepT) within ASD appears to be a broader construct than general rumination. Better understanding of the phenomenon, mechanisms, and health states associated with RepT in autism could determine novel, specific targets to guide development of health interventions for adults with ASD. Our proposal seeks to characterize repetitive thinking within ASD and inform its psychometric measurement in this population (Aim 1); explore neural correlates of sustained cognitive-affective processing in adults with ASD using pupil methods, with comparisons to typically developing depressed adults (TD-dep) (Aim 2); and investigate relations between diverse forms of RepT and health and behavior in adults with ASD (Aim 3). This work is intended to shape precision hypotheses as to which specific RepT processes most impact which adverse health outcomes in this special population. Aim 1 takes a mixed-method approach, including: (1) structural analyses of survey data on various constructs related to RepT (e.g., rumination, worry, obsessive thoughts, circumscribed interests) to identify common patterns of repetitive thinking (e.g., by valence, function, intrusiveness) in a large sample of verbally-fluent adults with ASD, n=760 online + n=72 in lab; and (2) lab- based inductions of RepT, with pre-/post language samples coded for RepT features. Findings will be synthesized to inform understanding of the phenomenon and measurement of RepT in ASD. In Aim 2, patterns of pupil-indexed neural reactivity will be compared across diagnostic cohorts (ASD and TD-dep) and stimuli types (social, non-social, emotional, non-emotional), and assessed for relation to RepT features and other moderators. This is intended to illuminate patterns of sustained cognitive-affective processing in ASD, and thus refine future research into mechanistic ?points of entry? for treatment development. Aim 3 proposes to analyze both existing and novel markers of diverse forms of RepT for differential association with health and functioning in adults with ASD. A model will be tested in which negative RepT predicts poor emotional and physical health, whereas positive/neutral RepT predicts social deficits. This proposal applies an expert team and multi-method approach to the goal of identifying potential targets for intervention on emotional health problems, which are prevalent and largely untreated in adults with ASD. If successful, this also will structure empirical data collection on RepT, advance understanding of its mechanisms via a convergent physiological marker (sustained pupil responsivity), and help extend repetitive behavior research to internal thinking processes.